1. Field of the Invention
This invention relates to a method of controlling an end sealing time period as long as possible for a longitudinal-type or a traverse-type bag forming, filling and packaging machine adapted to effect a box-motion type end sealing.
2. Description of the Related Art
A typical longitudinal-type bag forming, filling and packaging machine is constructed as shown in FIG. 1. A packaging film is introduced to a former 9 where the film is folded to wrap about a product filling cylinder 2 and to form a seam at the front side of the former 9. The seam is longitudinally sealed by a longitudinally sealing device 3 or 3' so that the film forms a packaging cylinder H. A film feeding device 4, located at a side of the product filling cylinder 2, pulls the packaging cylinder H downwardly so that the packaging cylinder 2 is located below the product filling cylinder 2. Then, an end-sealing (lateral-sealing)/cutting device 5 effects the end-sealing (lateral-sealing) and the cutting of the packaging cylinder H, so that a packaged product J is discharged. Although this end-sealing may be effected at a fixed position, such an arrangement is available that carries out a box motion as shown by a in order to elongate a sealing time period. The box motion makes it possible to move the end-sealing/cutting device 5 downwardly along a linear segment b in synchronous with the travel of the packaging cylinder without the stoppage of the travel of the packaging cylinder. That is, the sealing with a heater continues during the movement along the line segment b, the sealing time period can be elongated without any stoppage of the travel of the packaging cylinder. The content, such as confectionery, to be filled into the packaging cylinder is delivered downwardly through the product filling cylinder 2 during a return period c of the box motion of the end-sealing.
The operation of the end-sealing (lateral-sealing)/cutting device 5 will be described in detail. At the upper portion d of the linear segment of the box motion a, heaters for the end-sealing (lateral-sealing) are closed toward each other in conformity with a cut position of the packaging cylinder H. Prior to the complete close of the end-sealing heaters, two pairs of opposing shutters are closed to make the packing cylinder flattened. The opposing shutters in each pair are elastically held in such a manner as to protrude toward the mating shutter more closely than the right and left end-sealing heaters do, and the two pairs are respectively arranged at upper and lower sides of the right and left sealing heaters. The end-sealing heaters are thereafter closed completely to seal the packaging cylinder H at two lateral-rows simultaneously, while the cutter cuts the cut position (i.e. an intermediate position between the two lateral-rows). One of the lateral-row is located at the proximity of the upper side of the product to be packaged, which has been fallingly delivered and filled through the product filling cylinder, and the other of the lateral-row is located at the proximity of the lower side of the product to be packaged, which are to be fallingly delivered and filled subsequently.
The above-described box motion type end-sealing/cutting device is designed so that the pair of end-sealing heaters are moved along such loci (i.e. two arcuate loops a) that a pair of cam curves, each being formed by a circle partially cut at its one side with a linear segment, are opposed to the other. That is, the box motion type end-sealing/cutting device repeatingly makes such symmetrical box motion that a pair of end-sealing heaters are closed to each other to carry out the lateral two row sealing while being moved downwardly, and subsequently open widely while being returningly moved upwardly so as not to interfere with the product to be packaged after the cutter cuts the packaging cylinder at the cut position between the sealed lateral two rows. The two pairs of shutters, additionally provided to the box motion type end-sealing/cutting device, are not special ones, that is, they have the same structure as two pair of shutters additionally provided to a conventional end-sealing/cutting device which is not the box motion type device. The shutters simply function to be closed to each other and to make the packaging cylinder flattened prior to the complete close of the pair of the end-sealing heaters when the end-sealing/cutting device 5 makes the box motion to close the pair of end-sealing heaters.
The longitudinal type bag forming, filling and packaging machine suffers from a possibility that a packaging error occurs to bite a product to be packaged when the lateral-sealing is carried out by the pair of end-sealing (lateral-sealing) heaters since the product to be packaged may become bulky in a height direction or rebounded up after being fallen down. For this reason, the end-sealing/cutting device is additionally provided with a product-biting preventive device equipped with a pair of stripping plates, so that the pair of stripping plates strip the packaging cylinder over an area from the upper side to the lower side of the cut position to forcibly push the product to be packaged when the pair of the end-sealing heaters are open. Japanese Patent Application Laid-Open No. Sho. 58-195101, U.S. Pat. No. 5,203,145, U.S. Pat. No. 4,947,618, U.S. Pat. No. 4,663,917, Japanese Patent Application Laid-Open No. Hei. 5-330504, Japanese Patent Application Laid-Open No. Hei. 9-12003 and so on relate to product-biting preventive devices of end-sealing/cutting devices in conventional longitudinal type bag forming, filling and packaging machines. The operation of the box motion slightly differs depending on the structure of the above-noted stripping plates.
Japanese Patent Application Laid-Open No. Hei. 5-330504 discloses an example of the product-biting preventive device of this type as a proposal of an assignee of this application. The disclosed product-biting preventive device for a longitudinal type bag forming, filling and packaging machine equipped with a box-motion type end-sealing (lateral-sealing)/cutting device as described in Japanese Patent Application Laid-Open No. Hei. 5-330504 will be described with reference to FIG. 19. In the box-motion type end-sealing/cutting device, a pair of end-sealing (lateral-sealing) heaters 5a and 5b make a pair of symmetrical box motions (m1 and m2) restricted by curved cam lines. The product-biting preventive device is arranged so that it is separated from the end-sealing/cutting device, and that a pair of stripping plates make a pair of symmetrical and longitudinally elongated box motions (m3 and m4) restricted by two slide strokes. When the pair of end-sealing heaters 5a and 5b are returningly moved upwardly while being open widely, the pair of stripping plates 6a and 6b are moved upwardly in the vicinities of the insides of the pair of end-sealing heaters 5a and 5b while remaining open and then moved closer to each other to such a degree as to flatten the packaging cylindrical but not to clamp the packaging cylinder. When the pair of end-sealing heaters 5a and 5b are moved closer to each other while being moved downwardly from the upper, returned position, the pair of stripping plates 6a and 6b are moved downwardly so as not to interference with the end-sealing heaters, that is, the pair of stripping plates 6a and 6b make such a stripping motion as to forcibly push the product to be packaged below the cut position of the packaging plate by transferring the flattened position of the packaging cylinder from the upper side of the cut position to the lower side thereof. Then, the pair of stripping plates 6a and 6b and the pairs of shutters 7a and 7b are closed to flatten and clamp the packaging cylinder, the pair of end-sealing heaters 5a and 5b are closed to seal the packaging cylinder at two lateral-rows in the vicinities of upper and lower sides of the sealed position thereof, and the cutter 5c cut the packaging cylinder at the cut position. The pair of end-sealing heaters 5a and 5b, after moving a predetermined amount downwardly, are moved away from each other and then returningly moved upwardly.
The configuration of the cam for causing this box motion is shown in FIG. 21(b) which is the same as the configuration of the cam for causing a box motion in a conventional case where the stripping plates 6a and 6b are not provided. In the figure, the end heater starts the sealing at I, and completes the sealing at II. The section from I to II is a sealing section. Through the outer circumferential section from II to I, the end heater is returned to the sealing start point I.
FIG. 20 shows steps for explaining a correlation between the end-sealing/cutting device and a packaging cylinder flattening device in the above-described machine. Positions of end heaters 5a and 5b, a push cutter 5c, shutters 7a and 7b, swing fingers 64a and 64b and stripping bars 6a and 6b are changed in order of steps (a), (b), (c), (d), (e) and (f) in a circulated manner. In the step (a), the reference character m1 and m2 denote box motion loci depicted by clamp surfaces of the end heaters 5a and 5b; m3, m4, box motion loci depicted by the stripping bars 6a and 6b caused by swinging and upward and downward movement of the swinging fingers 64a and 64b; and p, a box motion locus depicted by the rear end portion of the push cutter 11. In the step (a), the end heaters 5a and 5b moving upwardly are open and on the mid-points of the ascending stroke, and the swinging fingers 64a and 64b are moved upwardly while remaining open so that the stripping bars 6a and 6b are passed in the proximity of the inside of the end heaters 5a and 5b and positioned slightly above the shutters 7a and 7b. In the step (b), the swinging fingers 64a and 64b are located at upper portions where the two stripping bars 6a and 6b clamp and flatten the packaging cylinder, and the end heaters 5a and 5b are open at upper positions. In the step (c), the stripping bars 6a and 6b clamping the packaging cylinder are moved downwardly to the substantially mid-points of the descending stroke at a speed much larger than a film feeding speed. In this step, air is introduced into the bag, and the product to be packaged, which is fallingly filled and occupies in the upper positions, is stripped and fallen downwardly, and thereafter the shutters 7a and 7b are closed so that the shutters 7a and 7b in cooperation with the stripping bars 6a and 6b ensures the flatness of the end-sealing portion of the packaging cylinder. Further, the end heaters 5a and 5b are closed at positions in conformity with a register mark printed on the packaging film to start the two-lateral-row sealing. After the shutters 7a and 7b have been closed, the product to be packaged subsequently is supplied above the shutters 7a and 7b. In the step (d), the shutters 7a and 7b, the end heaters 5a and 5b and the stripping bars 6a and 6b, which are all closed, are moved downwardly, and when the end heaters 5a and 5b are located at the substantially mid-points of the descending stroke, the push cutter 5c cuts a portion of the packaging cylinder between the two-lateral-row sealed portions. In the step (e), the shutters 7a and 7b, the end heaters 5a and 5b, and the stripping bars 6a and 6b, which all remain closed, reach the descended positions, and the push cutter 5c has already completed the push cutting and retracted. In the step (f), the shutters 7a and 7b, the end heaters 5a and 5b, and the stripping bars 6a and 6b are open to be returningly moved upwardly.
Next, a problem encountered in the art will be described with reference to FIG. 2 by describing an operation of the longitudinal type bag forming, filling and packaging machine disclosed by the Japanese Patent Application Laid-Open No. 9-12003 by way of example. FIG. 2 is a longitudinally sectional view.
The box motion, as depicted by curved cam lines m1 and m2 in FIG. 2, is created such that cam engagement followers of swinging levers 17 and 18 follow the curved cam lines m1 and m2 provided on circular plates rotated by rotating motion of a motor. The longer linear section (b in FIG. 1) of the box motion is more advantageous since the longer sealing time period can be ensured, but on the other hand, the longer linear section (the longer stroke) requires more volume of mechanical portions associated therewith and suffers from a likelihood of the mechanical vibration generated when the stroke is changed from the linear motion to the circular motion or vice versa. That is, the length of the stroke has an upper limit and thus the sealing time period has an upper limit.